Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2 (original) (raw)
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Uniform California Earthquake Rupture Forecast, Version 3 (UCERF3)--The Time-Independent Model
Bulletin of the Seismological Society of America, 2014
The 2014 Working Group on California Earthquake Probabilities (WGCEP14) present the time-independent component of the Uniform California Earthquake Rupture Forecast, Version 3 (UCERF3), which provides authoritative estimates of the magnitude, location, and time-averaged frequency of potentially damaging earthquakes in California. The primary achievements have been to relax fault segmentation and include multifault ruptures, both limitations of UCERF2. The rates of all earthquakes are solved for simultaneously and from a broader range of data, using a system-level inversion that is both conceptually simple and extensible. The inverse problem is large and underdetermined, so a range of models is sampled using an efficient simulated annealing algorithm. The approach is more derivative than prescriptive (e.g., magnitude-frequency distributions are no longer assumed), so new analysis tools were developed for exploring solutions. Epistemic uncertainties were also accounted for using 1440 alternative logic-tree branches, necessitating access to supercomputers. The most influential uncertainties include alternative deformation models (fault slip rates), a new smoothed seismicity algorithm, alternative values for the total rate of M w ≥ 5 events, and different scaling relationships, virtually all of which are new. As a notable first, three deformation models are based on kinematically consistent inversions of geodetic and geologic data, also providing slip-rate constraints on faults previously excluded due to lack of geologic data. The grand inversion constitutes a system-level framework for testing hypotheses and balancing the influence of different experts. For example, we demonstrate serious challenges with the Gutenberg-Richter hypothesis for individual faults. UCERF3 is still an approximation of the system, however, and the range of models is limited (e.g., constrained to stay close to UCERF2). Nevertheless, UCERF3 removes the apparent UCERF2 overprediction of M 6.5-7 earthquake rates and also includes types of multifault ruptures seen in nature. Although UCERF3 fits the data better than UCERF2 overall, there may be areas that warrant further site-specific investigation. Supporting products may be of general interest, and we list key assumptions and avenues for future model improvements. Manuscript Organization Because of manuscript length and model complexity, we begin with an outline of this report to help readers navigate the various sections: • Future Improvements 7. Conclusions and Recommendations 8. Data and Resources 9. Acknowledgments 10. References Except where noted, all magnitudes (M) referenced here represent moment magnitude. Spatial distribution of off-fault gridded seismicity set by choosing one of the spatial probability density maps SRP Scientific Review Panel
Bulletin of the Seismological Society of America, 2003
The moment magnitude M 7.8 earthquake in 1906 profoundly changed the rate of seismic activity over much of northern California. The low rate of seismic activity in the San Francisco Bay region (SFBR) since 1906, relative to that of the preceding 55 yr, is often explained as a stress-shadow effect of the 1906 earthquake. However, existing elastic and visco-elastic models of stress change fail to fully account for the duration of the lowered rate of earthquake activity. We use variations in the rate of earthquakes as a basis for a simple empirical model for estimating the probability of M Ն6.7 earthquakes in the SFBR. The model preserves the relative magnitude distribution of sources predicted by the Working Group on California Earthquake Probabilities' (WGCEP, 1999; WGCEP, 2002) model of characterized ruptures on SFBR faults and is consistent with the occurrence of the four M Ն6.7 earthquakes in the region since 1838. When the empirical model is extrapolated 30 yr forward from 2002, it gives a probability of 0.42 for one or more M Ն6.7 in the SFBR. This result is lower than the probability of 0.5 estimated by WGCEP (1988), lower than the 30-yr Poisson probability of 0.60 obtained by WGCEP (1999) and WGCEP (2002), and lower than the 30-yr time-dependent probabilities of 0.67, 0.70, and 0.63 obtained by WGCEP (1990), WGCEP (1999), and WGCEP (2002), respectively, for the occurrence of one or more large earthquakes. This lower probability is consistent with the lack of adequate accounting for the 1906 stress-shadow in these earlier reports. The empirical model represents one possible approach toward accounting for the stress-shadow effect of the 1906 earthquake. However, the discrepancy between our result and those obtained with other modeling methods underscores the fact that the physics controlling the timing of earthquakes is not well understood. Hence, we advise against using the empirical model alone (or any other single probability model) for estimating the earthquake hazard and endorse the use of all credible earthquake probability models for the region, including the empirical model, with appropriate weighting, as was done in WGCEP (2002).
2013
Fault section Change Comments Calaveras (No) 2011 CFM Revised Replaced WGCEP (2008) geometry with SCFM. Calaveras (So) 2011 CFM Revised Replaced WGCEP (2008) geometry with SCFM. Calaveras (So) Paicines extension Addition Addition based on SCFM, part of Paicines Fault. Camp Rock Addition Added based on Jennings and Bryant (2010) traces. Landers Fault section from UCERF2 disassembled into individual faults. Canada David (Detachment) Addition Addition from SCFM. Carlsbad Addition Addition from SCFM. Carson Range (Genoa) Addition Used 2008 USGS National Seismic Hazard Map parameters.
TIME-DEPENDENT SEISMIC HAZARD IN THE SAN FRANCISCO BAY REGION, CALIFORNIA
A key assumption in standard probabilistic seismic hazard analysis (PSHA) is that earthquake occurrence can be modeled as a Poisson process (time-independent). For but a few regions in the world, however, the timing information on past earthquakes are not sufficient to calculate time-dependent hazard. We have calculated time-dependent probabilistic hazard for the San Francisco Bay region (SFBR) resulting from the region's seven major faults (e.g., San Andreas, Hayward-Rodgers Creek) using the range of models that were considered by the Working Group on California Earthquake Probabilities (WGCEP, 2003). Based on their results, there is an increasing probability of a large (moment magnitude [M] > 6.7) earthquake occurring in the SFBR in the period 2002 to 2031. The estimated probability in 2002 was 62%. WGCEP (2003) considered five probability models that take into account various degrees of physics, date of last rupture, recent seismicity rates, and slip in the 1906 M 7.9 San ...
California Earthquake Rupture Models
2012
We present a stochastic earthquake source model for intermediate-to long-term forecasts. The model is based on fundamental observations: the frequency-magnitude distribution, slip rates on major faults, long-term strain rates, and source parameter values of instrumentally-recorded and historic earthquakes. The basic building blocks of the model are two pairs of probability density maps. The first pair consists of smoothed seismicity and weighted focal mechanisms based on observed earthquakes. The second pair contains the same type of information for faults. We construct from the model a “stochastic event set”, i.e. a large set of simulated earthquakes that are relevant for seismic hazard calculations and model testing. Their complete descriptions are determined in the following order: magnitude, epicenter, moment tensor, length, displacement, and down-dip width. Our approach assures by construction that the simulated magnitudes are consistent with the observed frequency-magnitude di...
A Synoptic View of the Third Uniform California Earthquake Rupture Forecast (UCERF3)
Seismological Research Letters
Probabilistic forecasting of earthquake-producing fault ruptures informs all major decisions aimed at reducing seismic risk and improving earthquake resilience. Earthquake forecasting models rely on two scales of hazard evolution: long-term (decades to centuries) probabilities of fault rupture, constrained by stress renewal statistics, and short-term (hours to years) probabilities of distributed seismicity, constrained by earthquake-clustering statistics. Comprehensive datasets on both hazard scales have been integrated into the Uniform California Earthquake Rupture Forecast, Version 3 (UCERF3). UCERF3 is the first model to provide self-consistent rupture probabilities over forecasting intervals from less than an hour to more than a century, and it is the first capable of evaluating the short-term hazards that result from multievent sequences of complex faulting. This article gives an overview of UCERF3, illustrates the short-term probabilities with aftershock scenarios, and draws some valuable scientific conclusions from the modeling results. In particular, seismic, geologic, and geodetic data, when combined in the UCERF3 framework, reject two types of fault-based models: long-term forecasts constrained to have local Gutenberg-Richter scaling, and short-term forecasts that lack stress relaxation by elastic rebound.
Short- and Long-Term Earthquake Forecasts for California and Nevada
Pure and Applied Geophysics, 2010
We present estimates of future earthquake rate density (probability per unit area, time, and magnitude) on a 0.1degree grid for a region including California and Nevada, based only on data from past earthquakes. Our long-term forecast is not explicitly time-dependent, but it can be updated at any time to incorporate information from recent earthquakes. The present version, founded on several decades worth of data, is suitable for testing without updating over a five-year period as part of the experiment conducted by the Collaboratory for Study of Earthquake Predictability (CSEP). The short-term forecast is meant to be updated daily and tested against similar models by CSEP. The short-term forecast includes a fraction of our long-term one plus time-dependent contributions from all previous earthquakes. Those contributions decrease with time according to the Omori law: proportional to the reciprocal of the elapsed time. Both forecasts estimate rate density using a radially symmetric spatial smoothing kernel decreasing approximately as the reciprocal of the square of epicentral distance, weighted according to the magnitude of each past earthquake. We made two versions of both the long-and shortterm forecasts, based on the Advanced National Seismic System (ANSS) and Preliminary Determinations of Epicenters (PDE) catalogs, respectively. The two versions are quite consistent, but for testing purposes we prefer those based on the ANSS catalog since it covers a longer time interval, is complete to a lower magnitude threshold and has more precise locations. Both forecasts apply to shallow earthquakes only (depth 25 km or less) and assume a tapered Gutenberg-Richter magnitude distribution extending to a lower threshold of 4.0.
Bulletin of the Seismological Society of America, 2015
The 2014 Working Group on California Earthquake Probabilities (WGCEP 2014) presents time-dependent earthquake probabilities for the third Uniform California Earthquake Rupture Forecast (UCERF3). Building on the UCERF3 time-independent model published previously, renewal models are utilized to represent elasticrebound-implied probabilities. A new methodology has been developed that solves applicability issues in the previous approach for unsegmented models. The new methodology also supports magnitude-dependent aperiodicity and accounts for the historic open interval on faults that lack a date-of-last-event constraint. Epistemic uncertainties are represented with a logic tree, producing 5760 different forecasts. Results for a variety of evaluation metrics are presented, including logic-tree sensitivity analyses and comparisons to the previous model (UCERF2). For 30 yr M ≥ 6:7 probabilities, the most significant changes from UCERF2 are a threefold increase on the Calaveras fault and a threefold decrease on the San Jacinto fault. Such changes are due mostly to differences in the time-independent models (e.g., fault-slip rates), with relaxation of segmentation and inclusion of multifault ruptures being particularly influential. In fact, some UCERF2 faults were simply too long to produce M 6.7 size events given the segmentation assumptions in that study. Probability model differences are also influential, with the implied gains (relative to a Poisson model) being generally higher in UCERF3. Accounting for the historic open interval is one reason. Another is an effective 27% increase in the total elastic-rebound-model weight. The exact factors influencing differences between UCERF2 and UCERF3, as well as the relative importance of logic-tree branches, vary throughout the region and depend on the evaluation metric of interest. For example, M ≥ 6:7 probabilities may not be a good proxy for other hazard or loss measures. This sensitivity, coupled with the approximate nature of the model and known limitations, means the applicability of UCERF3 should be evaluated on a case-by-case basis.
Journal of Geophysical Research: Solid Earth, 2018
An estimate of the expected earthquake rate at all possible magnitudes is needed for seismic hazard forecasts. Regional earthquake magnitude frequency distributions obey a negative exponential law (Gutenberg‐Richter), but it is unclear if individual faults do. We add three new methods to calculate long‐term California earthquake rupture rates to the existing Uniform California Earthquake Rupture Forecast version 3 efforts to assess method and parameter dependence on magnitude frequency results for individual faults. All solutions show strongly characteristic magnitude‐frequency distributions on the San Andreas and other faults, with higher rates of large earthquakes than would be expected from a Gutenberg‐Richter distribution. This is a necessary outcome that results from fitting high fault slip rates under the overall statewide earthquake rate budget. We find that input data choices can affect the nucleation magnitude‐frequency distribution shape for the San Andreas Fault; solution...